Closed circuit fluid apparatus for deep well pumping with counterbalance cylinder



Oct. 17, 1950 w. o. MILLER I 2,526,388

CLOSED CIRCUIT FLUID APPARATUS FOR DEEPVWELL PUMPING WITH COUNTERBALANCECYLINDER Filed July 30, 1945 4 Sheets-Sheet 1 A T TOE/V5 Y Oct. 17, 1950w. o. MILLER CLOSED CIRCUIT FLUID APPARATUS FOR DEEP WELL PUMPING WITHCOUNTERBALANCE CYLINDER 4 Sheets-Sheet 2 Filed July 30, 1945 mmvro e.Jim/ham 0H0 Mil/er 7 V/// M V/ Vy/// A TTOEA/EY w. o. MILLER 2,526,388CLOSED cmcurr FLUID APPARATUS FOR DEEP WELL Oct. 17, 1950 PUMPING WITHCOUNTERBALANCE CYLINDER 4 Sheets-Sheet 3 Filed Jul so, 1945 Dunn. Ann

.FIE 4 A TTOENE Y Oct. 17, 1950 2,526,388

W. O. MILLER CLOSED CIRCUIT FLUID APPARATUS FOR DEEP WELL PUMPING WITHCOUNTERBALANCE CYLINDER Filed July 30, 1945 4 Sheets-Sheet 4 0 I80 360DEGREES OF CRANK ROTATION FIE E .J g l K F z z- 2 7 2 n.

0 I150 360 DEGREES OF CRANK ROTATION INVENTOR. I 5 7 WIN/am 0/70 MH/er,4 TTOENE Y Patented Oct. 17, 195i) CLOSED CIRCUIT FLUID APPARATUS FORDEEP WELL PUMPING WITH COUNTER BALANCE CYLINDER William Otto Miller,Oakland, Calif., assignor of one-half to Ralph E. Cotter, Jr., Oakland,Calif.

Application July 30, 1945, Serial No. 607,713

(Cl. Gil-54.5)

Claims.

The present invention relates to pulsator devices and particularly toone suited to the pumping of oil wells, particularly those of greatdepth. The invention will be particularly described as it has beenapplied to the pumping of oil wells, but the pulsator device can be usedfor providing pulsating movement to other mechanism, particularly thosewhich present the problem of vertically reciprocating a relatively longrod having such weight that this is a factor in the pulsating of the rodand any system utilized in conjunction with the rod.

In wells of a few thousand feet in depth, no particular problem isinvolved and conventional rigs sufliee. However, as the length of thesucker rod in the well increases, its weight, plus the weight of thefluid lifted from the well, produces such an elongation or stretch inthe sucker 'rod that in many cases a relatively large movement of therod at the top end of the well must occur before any movement is appliedto the piston system in the region of the fluid in the well.

For example, and to give specific values, in one oil well pumping systemit was necessary to have a stroke at the top of the well ofapproximately 192 inches to provide a lift stroke at the end of thesucker rod of 48 inches. The difference of 144 inches was taken up instretching of the sucker rod and pump tubing.

It is my observation that to provide for proper motion and to secure thegreatest fluid output from the well per unit of power input, one mustprovide a cycle of motion of the sucker rod such that both ends of thesucker rod system operate in phase with each other. Stated differently,I

have observed that it is necessary that (a) the' stretching of a suckerrod and (b) the amplitude and frequency cycle of the stretch be in astate of motion known as harmonic motion." In'other words, the optimumcycle of sucker rod performance is such that both ends of the sucker rodsystem must operate in phase with each other.

It is difllcult, in long stroke straight line pumping'o'perations, toimpart harmonic motion to the sucker rod system. Even though harmonicmotion has been imparted to the top end of the sucker rod system in deepwells the bottom end is extremely difllcult to keep in phase with theupper end due primarily to the stretch in the sucker rod and tubingsystem. This troublesome condition is further amplified by the fact thatboth the sucker rod system and the deep well pump tubing have their ownnatural periods of vibration. The stretch and natural period ofvibration of each system can be determined from which the optimumfrequency and amplitude of sucker rod stroke can be determined. Byoptimum frequency and amplitude, I refer to the length of stroke andnumber of strokes per minute in addition to the type of motion impartedto the top of the polish rod in the sucker rod system to satisfy theengineering and economic factors involved in any given case.

It is in general the broad object of the present invention to provide animproved device for the pumping of deep oil wells and the like.

A further object of the present invention is to provide means forimparting harmonic reciprocating motion to a sucker rod system.

The present invention contemplates utilization of a closed fluid systemincluding the use of two cylinders and a movable piston in eachcylinder. One piston is mounted upon the top end of the sucker rodsystem, i. e., on the end of the polish rod, while the other piston isadapted to be moved in a pulsator cylinder in a manner which I willpresently discuss in further detail. 4 Corresponding ends of eachcylinder are connected one to another so that when the piston in thepulsator cylinder is moved in one direction a non-compressible fluid isforced positively into the other cylinder to cause the other piston tomove the sucker rod in an opposite direction, the fluid on top of thepiston in the sucker rod cylinder being displaced. The means employedfor moving the pulsator piston imparts a harmonic reciprocating motionto that piston. since the. fluid system provided on each side of eachpiston is of constant volume, it will be obvious that harmonic motionwill be. applied from the pulsator piston to the piston in the sucker orpolish rod cylinder. Also, by employinga pulsator piston of large areamoved over a relatively short distance one can move a fluid volumesufllcient to provide a long stroke on a sucker rod piston of a suitableand a small area. In this way, the practical requirements of pump designcan be observed while the long stroke required to pump the well is madeavailable. Further, and in accordance with this invention,

the pulsator piston is moved at such a rate that the requisite harmonicmotion is applied to the sucker rod piston and the sucker rod system.

The invention includes other objects and features ofadvantage some ofwhich, together with the foregoing, will appear hereinafter wherein,referring to the drawing, a preferred form of a harmonic motion suckerrod system is dismissed;

Referring to the drawing accompanyin and forming a part hereof,

Figure 1 is a side elevation showing the pulsator and sucker rodinstallation.

Figure 2 is a section taken through the pump mechanism along the line2-2 in Figure 1.

Figure 3 is a section taken along the line 33 in Figure 2 and showing aScotch yoke or crosshead, crank, crankpin and shaft assembled in thecrankcase.

Figure 4 is a section taken along the line 4-4 in Figure 3 and showingdetails of the crank.

Figure 5 is a section through the center line of the sucker rod pistonand cylinder assembly.

Figure 6 is a graph showing the comparison between the reciprocatingmotion produced by a Scotch crosshead and a conventional crank andconnecting rod.

Figure 7 is a, graph showing the comparison between the travel of thepulsator piston and. the sucker rod piston.

Referring to the drawing, an oil well casing is generally indicated bynumeral 5, the casing being closed as at 1 and being provided with apacking gland 3 through which issues the polish rod 8. An oil outlet His also provided from the casing. Mounted upon a suitable foundation I2is a support structure l4 upon which is mounted sucker rod cylinder I8.

Polish rod 9 extends into hollow piston rod 39 and is clamped thereto byclamp 40. Piston rod 39 carries a suitable piston H. In the event thatthe sucker rods are to be pulled from the well, the internal diameter ofpiston rod 39 is such that the rods may be pulled through the piston rodand removed without dismantling the pumping equipment that standsdirectly over the well. This installation lends itself to thepossibility of utilizing the power made available by cylinder IS inlifting the several sucker rod lengths from the well.

Pipes l8 and i9 extend from opposite sides of sucker rod cylinder IE topulsator cylinder 2| mounted upon the crankcase 53 and which, in turn,is mounted upon a foundation structure 23. The pulsator cylinderincludes a piston 24 therein mountd upon a piston rod 26. The piston rod26 extends beyond cylinder 2| and carries upon its upper end a secondpiston 21 slidable in a cylinder 28, the latter being open at its lowerend as at 29, and closed at its upper end except for a lead-off line 30.The function of cylinder. 28 on piston 21 will be presently discussed.

To move pulsator piston 24, a suitable prime mover assembly 3| isprovided including electric motor 32 or other suitable prime moverdriving a gear reducer 33 through drive 34, shaft 36 from the reducerdriving a shaft 31. in the crankcase 53, and which is shown particularlyin Figures 3 and 4. A crank 4| is fixed to shaft 31 by key I 42 while aslotted crank block 54 is fixed to the crank 4| by machine screws 55.Crank block 65 is fixed similarly to auxiliary crank 45. Crank pin 43 isfixed to crank block 54 by set screw 44 and to auxiliary crank block 65by set screw 46. Auxiliary crank 45 is fixed to auxiliary shaft 41 bykey 48. Crank pin 43 revolves in crosshead block 43 which slides in slot50 of crosshead 5|.

As shaft 31 is rotated by the prime mover assembly 3|, crank 41 impartscircular motion to crank pin 43. This forces block 43 to reciprocate inslot 50, in turn imparting reciprocating motion in a vertical plane tocross head 5| which slides between guide surfaces 52 of crankcase 53.Crosshead 5| is fixed to shaft 26 thereby imparting its motion to piston24. As crank 4| revolves, the distance which crankpin 43 moves, measuredin a horizontal direction, is the same as the vertical movement of thecrosshead 5|. This is a simple and well known mechanism for producingtrue harmonic motion, as contrasted with the common crank and connectingrod which combination does not produce harmonic motion.

The length of stroke of crank 4| may be adjusted by inserting slottedblocks 54 and in any desired set of slots 56 in crank 4| when screws 55,which hold blocks 54 and 55 in position, are removed. Any change inlength of crank stroke will change the stroke of piston 24 by anequal-amount. This change is then reflected in the stroke of piston H byan amount proportional to the ratio of the respective piston net areas.For proper lubrication, crankcase 5| is partially filled withlubricating oil through plug 58. Shafts 31 and 41 revolve in bearings 20and 22, respectively, which are mounted in openings in bearing housings84 and 35, respectively, and held by plates 86 and 61, respectively, andscrews 68. If a more uniform application of force to block 49 isdesired, power may also be 'applied to an extension of shaft 41.

The area of the pulsator piston 24 and its stroke in the pump cylinder2| is such that the same volume of fiuid is displaced from the pump oneach stroke as is displaced in the sucker rod cylinder.

Through the use of different cylinder diameters it is possible to obtaina long sucker rod stroke while maintaining a short pulsator stroke.Since the value of fluid handled remains constant regardless of strokeor cylinder diameter ratios, it is axiomatic that the actualdisplacement of each piston is always equal.

For purposes of illustration I offer the follow- Let S equal length ofstroke of sucker rod piston Let A equal net area of sucker rod pistonLet X equal length of stroke of pulsator Let Y equal net area ofpulsator piston In every case the product of the values of S multipliedby A must be equal to the product of the values of X multiplied by Y.The greatest value of this invention is attained when the value of S isgreater than the value of X. However, engineering considerations enterinto the choice of the value of X for any given value of Sfor example:

S equals 20 ft.assumed for a hypothetical case A equals 1 sq. ft. netarea-assumed for a hypothetical case.

For the above values of S and A, good engineering has established avalue of X to be of the order of 5 ft.

Since S times A must always be equal to X times Y, Y equals S times Adivided by X or, substituting values,

For practical application, the values of SA,X and Y may be determinedattention being given to the required value of S for any given pumpingoperation. In every case the product of the value of S multiplied by thevalue of A must be equal to the product of the value of X times thevalue of Y as was borne out by the values given in the apparatus abovedescribed.

In one structure the net area of the pulsator piston was 500 squareinches while that of the eases of the pulsator piston was 20-incheswhile the stroke of the ram piston was 100 inches. It will be observedthat 10,000 cubic inches were displaced from each cylinder upon movementof each piston from one end of the associated cylinder to the oppositeend. Depending upon the direction of movement, the displaced fluid wastransferred from. one cylinder to the other through lines I! and I9.

' Energy loss upon fluid transfer is kept to a minimum by using conduitsof a suitable size. Thus the system provides. for imparting astraight-line motion to the sucker rod, but the rate of supply of thismotion is such as to impart the generally desired harmonic motion to thesucker rod system. The equipment required for this is quite simple andof standard construction.

Cylinder 28 and piston 21 provide a pneumatic counter-balance, air beingcompressed upon the upstroke of the piston which is utilized on thedownstroke to help raise the sucker rod system. The weight of the suckerrod system on the upstroke of the pulsator piston 24 assists incompressing air in the cylinder so that some advantage is gained fromthis energy.

The pneumatic counterbalance is adjustable to any desired initial andterminal pressure. The desired initial air premure is applied tocylinder 28 through air supply line 30 as measured by gauge 51 whenpiston 21 is at the bottom. of its stroke. The cylinder volume requiredabove the piston at the top of its stroke to produce the desiredterminal pressure is'then computed. This volume is acquired by adding orremoving a spacer 59 of required thickness or a flanged length ofcylinder (not shown), or by suitably adjusting the position of piston 21on shaft 26.

All free space in cylinders 2i and I6, conduits l8, I9, 62, and 63, andvalves BI and are completely fllled with a suitable non-compressiblefluid, suitable plugs 60 being provided for purposes of filling thesystem with fluid and permitting air to escape during the fillingoperation. A suitable plug 69 being provided for purposes of drainingthe fluid system. Pressure switches 64 6 90 degrees and 270 degrees ofcrank rotation, the velocity or rate of motion is at its maximum andthat the increments of acceleration and deceleration between zero and180 degrees of crank rotation are duplicated in reverse order but in thesame magnitude from 180 degrees to 360 degrees of crank rotation. Thepulsator piston is therefore moving in what is known as simple harmonicmotion. This motion can be placed in an harmonic phase with the naturalvibration period of the sucker rod system. The sucker rod system may belikened to a huge spring. Now it is commonly known that normal ornatural vibration of a spring occurs as simple harmonic motion. Anyother motion imparted to a spring or, in this case, to the sucker rodsystem, will be out of harmonic phase and therefore undesirable. In deepwell pumping, the sucker rods are stressed close to their ultimatestrength and any irregular motion will add additional stresses and leadto the failure of the rods. Harmonic moof a sucker rod system iscalculated by well known methods, attention being given to the length ofthe rod, its diameter, the area of the wellpump are provided to functionin the nature of safety devices arranged to stop the prime mover ,when

a predetermined pressure, considered to be unsafe. is attained in linesl8 or l9.

In operation, fluid passes alternately between cylinders 2i and I6through conduits I8 and IS with valves 6| open and bypass valves 10closed,

the fluid in the system serving to transmit energy from the pulsatorcylinder 2| to the ram cylinder l6 and vice versa. The bypass conduits62 and 63 and bypass valves 10 are provided only for purposes of initialadjustment of the fluid is always directed toward a fixed point inthepath of motion and in which the magnitude of the acceleration isproportional to the distance between the moving point and the fixedpoint, the moving point in this case being the piston and the fixedpoint being the top or bottom of the stroke, This curve indicatesclearly that at piston and its stroke and the gravity of the fluidpumped. The prime mover and its associated transmission device areadjusted to provide this optimum reciprocation. By measuring the rodstretch and by taking an expansion and contraction diagramfrom the topof the sucker rod, by well known means and methods, one can determine ifthe number of reciprocations per minute is that most advantageouslyemployed, 1. e., is the rod being moved at a rate consistent with itsown period of vibration. If it is not, the prime mover can be speeded upor the drive ratio between it and the pump shaft can be changed.

Curve B in Figure 6 shows the relationship between per cent of pumpstroke and degrees of crank rotation for a piston driven by an ordinaryconnecting rod. It clearly indicates that the relative motion betweenthe pulsator piston and crank during the first half of the stroke, thatis from F to G, is different from that of the second half, from G to H.This difference in motion, while not of apparent great magnitude on thediagram, is most undesirable since it is out of harmony with any naturalperiod of vibration of the sucker rod system; furthermore, theacceleration and deceleration never take place in a state of simpleharmonic 7 motion during the entire stroke cycle. This state of motiondoes not readily lend itself to being put in harmonic phase with thenatural vibration period of the sucker rod system. The remainder of thestroke cycle from H to I and I to J is similarly affected.

Curve C in Figure 7 is a curve of one cycle of pump piston travelplotted against degrees of crank rotation for a. representativepulsator. It is a curve of simple harmonic motion similar to curve A.Curve D is a curve of sucker rod piston travel for the same equipmentand shows how the harmonic motion is transferred to and is amplified inthe sucker rod piston. The amplified stroke of the sucker rod piston isbrought about by having the sucker rod piston net area less than thepulsator piston net area.

I claim:

1. In combination, a relatively long rod positioned vertically, a firstpiston on said red, I. first cylinder cooperatively positioned withrespect to asaaaee said first piston and in which said first piston ismovable to raise and lower said rod, a pulsator cylinder, a pistonmovable in said pulsator cylinder ona piston rod, a counter-balancecylinder, a counter-balance piston on saidpiston rod and movable in saidcounter-balance cylinder, means for controlling fluid pressure in saidcounter-balance cylinder to counter-balance at least a substantialportion of the dead-weight load of the rod and the piston thereon, thearea of said pulsator piston being relatively large as compared to thearea of said first piston, the stroke of said first piston beingrelatively large as compared to said pulsator piston stroke, a firstconduit connecting one end of said pulsator cylinder to one end of saidfirst cylinder, a second conduit connecting the other end of saidpulsator cylinder to the other end of said first cylinder, and means formoving said pulsator piston back and forth in said pulsator cylinder ata rate substantially corresponding to a rate designated as harmonicmotion.

2. In combination, a relatively long rod positioned vertically, a firstrod, a first cylinder cooperatively positioned with respect to saidfirst piston and in which said first piston is movable to raise andlower said rod, a pulsator cylinder, a pulsator piston movable in saidpulsator cylinder on a piston rod, a counter-balance cylinder, acounter-balance piston on said piston rod and movable in said cylinder,means for controlling fluid pressure in said counter-balance cylinder tocounter-balance at least a substantial portion of the dead-weight loadof the vertical rod and the first piston, the area of said pulsatorpiston being relatively large as compared to the area of said firstpiston, the stroke of said first piston being relatively large ascompared to said pulsator piston stroke, a first conduit connecting oneend of said pulsator cylinder to one end of said first cylinder, 9.second conduit connecting the other end of said pulsator cylinder to theother end of said first cylinder, a liquid filling said cylinders andsaid conduits, and means for moving said pulsator piston back and forthinw said pulsator cylinder to deliver fluid to said first cylinder andmove the first piston therein at. a rate substantially corresponding toa rate designated as harmonic motion, the liquid volume displaced fromsaid pulsator cylinder upon movement of the pulsator piston therein fromone extreme of travel to the other extreme being equal to the liquidvolume displaced from the first cylinder upon movement of the firstpiston from one extreme to the other.

3. In combination, a relatively long vertical rod, a first piston onsaid vertical rod, a first cylinder cooperatively positioned withrespect to said first piston and in which said first piston is movableto raise and lower said vertical rod, a pulsator cylinder, a pulsatorpiston movable in said pulsator cylinder on a piston rod, acounterbalance cylinder, a counter-balance piston on said piston rod andmovable in said cylinder, means for controlling fiuid pressure in saidcounter-balance cylinder to counter-balance at least a substantialportion of the dead-weight load of the vertical rod and the firstpiston, a first conduit connecting one end of said pulsator cylinder toone end of said first cylinder, a second conduit connecting the otherend of said pulsa- 8 tor cylinder to the other end of said firstcylinder, and means for moving said pulsator piston back and forth insaid pulsator cylinder at a rate substantially corresponding to'a ratedesignated as harmonic motion.

4. In combination, a long vertical rod, a first piston on said verticalrod, 9. first cylinder cooperatively positioned with respect to saidfirst piston and in which said first piston is movable to raise andlower said vertical rod, a pulsator cylinder, a pulsator piston movablein said pulsator cylinder on a piston rod, a counter-balance cylinder, acounter-balance piston on'said piston rod and movable in saidcounter-balance cylinder, means for controlling fiuid pressure in saidcounter-balance cylinder to counter-balance at least a substantialportion of the dead weight load of the vertical rod and the firstpiston, the area of said pulsator piston being relatively large ascompared to the area of said first piston, the stroke of said firstpiston being relatively large as compared to said pulsator pistonstroke, a first conduit connecting one end of said pulsator cylinder toone end of said first cylinder, at second conduit connecting the otherend of said pulsator cylinder to the other end of said first cylinder,and means for moving said pulsator piston back and forth in saidpulsator cylinder at a rate substantially corresponding to a ratedesignated as harmonic motion and including a rotatable shaft, and aScotch yoke interposed between said shaft and said pulsator piston.

5. In a hydraulic pulsator, a pulsator transmitter cylinder, a pulsatorpiston movable in said cylinder on a piston rod, a counter-balancecylinder, a counter-balance piston on said piston rod and movable insaid counter-balance cylinder, means for controlling fluid pressure inthe said counter-balance cylinder to counter-balance a substantialportion of an unbalanced load driven by said pulsator, and means fordriving said pistons in said respective cylinders.

, WILLIAM O'I'IO MILLER.

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